Today I went to ride the Quarter Horse Appendix I've been riding, and she'd been in her stall all morning and most of yesterday (was out for an hour or so). I knew she had some energy so didn't want to get right on her. So I decided to let her loose in the indoor arena for a bit. I took her out and encouraged her into a trot with the end of my lead rope near her (not hitting her with it of course). She went right up into one and I immediately stopped, but she had so much energy she went right up into a canter and took off around the arena. She did some kicks and then started to gallop. This isn't a huge arena, and I started getting worried at this point. She came skidding to a stop a few times, then took a turn too fast and ended up doing a sliding fall (I was not encouraging her forward at all here, it was all her). The footing is sand/rubber with a cement bottom. She got right back up and took off again seemingly unfazed. I finally got her to stop by going over to the gate to outside where she came up to me.
Now, I know lots of people let their horses loose to let off a little steam, but this was out of control. Was I really stupid to let her loose like that? I don't plan to in the future, or if I do, in the much larger outdoor arena. If I need her to let off some steam I'm planning to let her out in her pasture for a few minutes instead. I'm not skilled enough in lunging her when she has that much energy, and she doesn't have much practice with it yet. I'm working on building my skills.